The three astronauts on the International Space Station are having ice cream for dessert tonight — and we're not talking about that spongy "astronaut ice cream" stuff. This is the vanilla chocolate-swirl ice cream that was delivered in a research freezer aboard the SpaceX Dragon cargo ship that arrived on Wednesday.

"It's quite a treat," space station commander Sunita Williams told ABC News during a space-to-Earth interview today. "We don't usually have this type of stuff up here. It's usually thermostabilized or dehydrated [food] that we're dehydrating. So homemade ice cream is something special, and we're going to have a little party."

The Blue Bell ice cream was a late addition to the manifest for SpaceX's Dragon supply flight, which marks the first routine commercial cargo delivery under the terms of a $1.6 billion, 12-flight contract with NASA. Astronauts used the space station's arm to bring the Dragon in for berthing early Wednesday, and the time line went so smoothly that the hatches between the station and the visiting spacecraft were opened that same day — a day earlier than scheduled.

The ice cream was transferred from the Dragon's ultra-cold GLACIER research freezer to the space station's own freezer space in preparation for tonight's dinner. Williams is sharing the treats with Japanese astronaut Aki Hoshide and Russian cosmonaut Yuri Malenchenko. NASA spokesman Rob Navias told me today that the ice cream supply amounts to a pint or two — and it's not clear how long the spacefliers will be able to stretch that out. "It depends on how much they eat," Navias quipped.

The space station's crew has until Oct. 28 to transfer 882 pounds (400 kilograms) of supplies into the station, load it back up with about twice as much mass in Earth-bound cargo, and unberth the Dragon for its re-entry and splashdown. In place of the ice cream, the GLACIER freezer will be carrying frozen biological samples, including hundreds of frozen blood and urine samples that have been waiting for a ride back down to Earth. Since last year's retirement of the shuttle fleet, the Dragon is the only spacecraft capable of returning a significant amount of cargo from the space station.

Navias made it sound as if Williams and her crewmates should have no problem meeting their deadlines.

"As of 1 p.m. Central Time, the crew had completed 77 percent of all of the cargo transfer and had already unpacked all of that cargo moved over to the station so far," Navias told me in a follow-up email. "All in one day. Way ahead of schedule."

Sounds like somebody deserves an extra helping of ice cream.

Update for 5 p.m. ET: NASA's Space Food Hall of Fame notes that the freeze-dried confection known as astronaut ice cream actually flew in space only once, aboard Apollo 7 in 1968. "It wasn't that popular," NASA food scientist Vickie Kloeris said in 2005. The desserts offered to the space station's astronauts are typically things like chocolate brownies, plum-cherry cobbler, honey cake or berry medley. Every once in a while, though, a space shuttle shipment would include real ice cream as a special treat.